The present invention relates to a pressing tool for producing dish-shaped pressed objects, in particular plates, cups, bowls, etc., of powdery, preferably ceramic material, comprising a die and a counterdie whose front surfaces facing each other form the upper and lower sides of the dish-shaped pressed object when the powdery material filled in therebetween is pressed, the die and counterdie being adapted to move toward each other and the powdery material being filled into a space limited by the front surfaces of the die and counterdie and an annular element having a connection for the feeding of material, said element being displaceable relative to the die and counterdie in their direction of movement toward each other, and at least one of the rims of the front surfaces of the die and counterdie protruding in an annular shape toward the rim of the other front surface, and the die and counterdie being adapted to move toward each other only so far as to leave a small axial annular gap between the rims of their front surfaces.
Such a pressing tool is disclosed in EU Pat. No. 0 043 019. The material to be pressed is filled in by aid of gravity in the case of this pressing tool. Due to the relatively small filling slot, the filling process is relatively slow. In the case of parts having steep walls, vertical walls and/or walls with a relief structure, there is a danger of the filling process being interrupted, or at least being uneven, because the effect of gravity is partly balanced out by the frictional forces acting on the material being filled.
The invention is based on the problem of redesigning the known pressing tool so as to make it possible to fill in material by aid of underpressure applied to the filling space. However, the advantage of the known teaching must be retained, i.e. that deficient pressed objects due to deficiencies in the filling process are avoided and reworking can also be dispensed with because the pressed object directly obtained is a formation having rounded rims.
Filling by aid of underpressure or a vacuum is actually already part of prior art. According to German Pat. No. 31 01 236, filling is effected by adding the material to be pressed within the limits of the rim of the die-formed part. This means that marking in the area where material is filled in can basically not be avoided, so that one is forced to replace the filling head by a smooth-rimmed pressing head or to remove the pressed on markings again by elaborate reworking.
It is also already disclosed in German offenlegungsschrift No. 31 44 678 to effect the filling from the rim. But the displaceable annular element is a shaping element here and must therefore be designed in a way corresponding to the desired rim of the plate.
It is further disclosed in German offenlegungsschrift No. 31 26 155 to fill the press via a vacuum pipe opening out in the filling area out of a funnel surrounding this assembly. However, this is in practice gravimetric filling into a closed space, which does not ensure even filling since the corresponding closing elements must be closed at the same time. Furthermore, predosing is required, which does not ensure suction through the vacuum channels.